1. Field of the Invention
This invention relates to thermoplastic polymer alloy compositions useful in wire and coating applications. This invention specifically relates to polyphenylene sulfide alloy compositions that are useful in wire coating applications requiring high temperature resistance and flame retardancy.
2. Description of Related Art
Temperature requirements for the insulation materials of wire and cable used under the hood of today""s high performance cars continue to increase. Thermoplastic polyvinyl chloride (PVC) used in high volume in automotive wiring provides chemical and flame resistance, insulation capability, and reasonable toughness, but suffers from higher temperature capability and environmental concern. The difficulties of disposal and recycle of PVC resin are recognized as serious problems today. Incineration results in formation of significant quantities of hydrogen chloride and heavy metal residues. Additionally, PVC is not compatible with other plastics used in manufacture of automobiles, which creates problems during recycling operations.
Today""s automotive wiring requires high temperature capability, good chemical and flame resistance, good electrical properties, good low temperature flexibility, and toughness. WO 93/08234 (Hausmann), published Apr. 29, 1993, provides a partially grafted, flexible thermoplastic blend based on polyester thermoplastic, epoxy group-containing ethylene copolymer, and ionomer of an acid group-containing ethylene copolymer with high and low temperature capability but poor flame resistance. Addition of halogen can provide flame resistance but introduces the environmental issue described above.
Crosslinked ethylene vinyl acetate copolymers (EVA) filled with hydrated fillers provide flame retardancy without halogen but modest mechanical toughness precludes thin automotive coatings for space savings in today""s tightly configured engine compartments. Crosslinking by either peroxide or irradiation adds cost. In the case of peroxide crosslinking, capital equipment such as a continuous vulcanization (CV) tube is required in contrast to thermoplastic systems.
Polyphenylene sulfide (PPS) is a high temperature, semicrystalline, engineering thermoplastic with excellent chemical resistance, high heat deflection temperature, good electrical insulation properties, and inherent flame resistance without halogen. Its poor flexibility can be seen in low impact strength and low elongation at break. Thus, PPS use has been limited in wire and cable applications that require high temperature capability, impact resistance, and flexibility, such as wiring under the hood of automobiles.
Toughened alloy compositions formed by melt blending certain ethylene copolymers certain polymeric grafting agents which contain reactive groups selected from at least one of epoxides, isocyanates, aziridine, silanes, alkyl halides, alpha-halo ketones, alpha-halo aldehydes, or oxazoline, along with a polymer selected from polyethylene, polypropylene and copolymer thereof, poly(butene-1), poly-4-methylpent-1-ene, polystyrene and copolymers thereof, polyphenylene oxide, polyphenylene sulfide (PPS) and polysulfone, are taught under U.S. Pat. No. 4,871,810 (Saltman).
Higher modulus alloys compositions containing PPS are disclosed in U.S. Pat. No. 5,625,002 (Toray). Neither Saltman nor Toray address suitable polyphenylene sulfide alloy compositions for flexible, high temperature, flame retardant applications such as wire and cable.
Consequently, there is a need in the art for a flexible, tough thermoplastic composition with low and high temperature capability, good electricals, and flame retardancy, preferably without halogen, for use in wire and cable applications, particularly automotive, under-the-hood wiring.